It is well known in the prior art that single-acting reciprocating-type hydraulic pumps produce a hydraulic fluid output having a varying pressure. This pressure variation varies cyclically with the stroke action of the reciprocating piston found in such pumps. For example, during the discharge stroke, the piston is pumping fluid from the pump, causing the maximum pressure to be generated in the hydraulic fluid, while during a return stroke, the pump output pressure tends toward zero as the pump is recharged with a fresh charge of hydraulic fluid to be pumped during the next power stroke of the piston. In most applications, it is impractical to provide a single cylinder hydraulic pump of sufficient capacity to supply all of the hydraulic fluid requirements during a single stroke. On the other hand, it is also impractical to operate a hydraulic system where the pressure is varying between maximum pressure and zero pressure, due to the fact that this would cause undesirably erratic and intermittent operation of the hydraulic apparatus supplied by such a pump.
Therefore, various alternatives have been developed in an attempt to provide necessary flow of hydraulic fluid in a manner which is constant in both volume and pressure. One such approach involves the use of a hydraulic pump apparatus having a plurality of pumping pistons which are cooperatively timed to provide the maximum discharge from each piston at a time differing from the other pistons so as to approximate a reasonably constant flow and pressure output in the hydraulic fluid. However, such multi-cylinder pumps include a substantially greater number of components, increasing both the initial cost and the cost of ongoing maintenance of such pumps, as well as increasing the likelihood that the hydraulic apparatus will suffer downtime due to pump failure.
In order to reduce the number of cylinders required in such pumps to provide a reasonable approximation of constant pressure output and volumetric flow, it has become a common practice to provide an accumulator to dampen the variations in pressure and flow from the pump to the hydraulic load. However, the typical accumulator is simply a container for accommodating volumetric variations resulting from changes in pressure and volumetric flow rate. In such accumulators, the pressure variations and volumetric flow variations are not actively damped, and as a result, such accumulators are often inadequate to provide the desired constant pressure and flow rate. There have been attempts in the prior art to provide active accumulators for hydraulic pump apparatus for the purpose of overcoming this deficiency. For example, accumulators have been provided which include a motor or solenoid means responsive to a controller. However, such accumulators merely respond to the pressure variations developed by the pump during the pumping cycle, and are not adequate to respond to the hydraulic load requirements and provide a continuous discharge of hydraulic fluid at the appropriate pressure and volumetric flow level. Such accumulators cannot accommodate the continuous demand of the hydraulic load for hydraulic fluid even when the hydraulic pump is not providing fluid to the accumulator.
Another attempted solution includes the use of a compensator having a free floating piston operating in response to a gas pressure supply in opposition to the pressure exerted by the hydraulic fluid. While such a compensator provides an improved means for compensating for pressure variations due to the continuous operation of the reciprocating pump, the compensator does not cooperate with the hydraulic pump to ensure that sufficient fluid is available to meet the hydraulic load requirements. This limits the usefulness of such a compensator to situations where the hydraulic load is a known constant, such that the compensated output from the hydraulic pump is sufficient to meet the hydraulic load demand. However, it is well known in the prior art that hydraulic load requirements tend to vary from application to application as well as varying during the use of the hydraulic apparatus in any given application.
Therefore, it is an object of the present invention to provide a reciprocating pump apparatus including an accumulator which will permit the hydraulic apparatus to respond to varying load conditions.
It is another object of the present invention to provide such a hydraulic apparatus as will employ a relatively small number of components.
It is yet another object of the present invention to provide such a hydraulic apparatus as will be relatively inexpensive to manufacture.
It is yet another object of the present invention to provide such a hydraulic apparatus as will provide a constant pressure and volumetric flow output from a single-cylinder hydraulic pump.
It is yet a further object of the present invention to provide such a hydraulic apparatus as will provide a means for controllably varying both the volumetric flow output and the hydraulic pressure output of the hydraulic apparatus while providing a relatively pulse-free fluid flow.
These and other objectives of the present invention will become apparent in the specification and claims that follow.